Listen as glass artist William Gudenrath describes the technique of making a core-formed vessel. The technique of core forming, which was introduced around the middle of the 16th century BC, was used to fashion some of the first glass vessels. Core forming involves the application of glass to a removable core supported by a rod. There is no consensus about how this was accomplished. Some scholars believe the glassmaker wound trails (strands) of molten glass around the core, or dipped the core into molten glass. Others suggest that a paste of powdered glass was applied to the core and fused with heat. After forming, the object was removed from the rod and annealed (slowly cooled to room temperature). Once the object had been annealed, the core was removed by scraping.